<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>

  <style>
    #app {
      width: 0px;
      height: 0px;
      /* background-color: red; */
      border-top: 20px solid transparent;
      border-bottom: 180px solid rgb(9, 255, 0);
      border-left: 100px solid transparent;
      border-right: 100px solid transparent;
    }
  </style>
</head>

<body>
  <div id="app"></div>
</body>

</html>